1. Field of the Invention
The present invention relates to a D/A converter, in particular a resistor string type D/A converter.
2. Description of Related Art
In recent years, high resolution in excess of 10 bits as well as high accuracy and cost reduction have been required in the field of D/A (Digital to Analog) converters.
In particular, resistor string type D/A converters employing a higher-order and lower-order division scheme and resistor string type D/A converters using an interpolation amplifiers are methods capable of realizing both high resolution and reduction in size simultaneously.
Japanese Unexamined Patent Application Publication No. 2008-85711 discloses a resistor string type D/A converter employing a higher-order and lower-order division scheme. FIG. 5 shows a configuration example of the resistor string type D/A converter employing a higher-order and lower-order division scheme disclosed in Japanese Unexamined Patent Application Publication No. 2008-85711. FIG. 5 shows a case where input data of 10 bits in width is divided into higher 8 bits and lower 2 bits.
In FIG. 5, two switches 51H and 51L for H(High) and L(Low) respectively are connected to respective voltage drawing points 502 at both ends of respective resistors 501 of the higher-order resistor string 50. Further, the lower 2-bit D/A converter 52 is composed of a resistor string 520 composed of four resistors 5202, and a selector 522. Further, the connection points 5201 between respective resistors 5202 and a signal line VL are connected to respective switches 521.
With the configuration like this, one of the switches 51L for Low and the switch 51H for High connected to the connection point 502 immediately higher than that switch 51L are turned on by the selector 53 based on higher 8 bit data, and a pair of voltages corresponding to the higher 8 bits are thereby supplied through the signal lines VH and VL. Then, one of the switches 521 is turned on by the selector 522, and a voltage that is specified by the lower 2 bits is thereby output. Therefore, an analog voltage according to a digital signal of 10-bits in width is output as a whole, and thus a 10-bit D/A conversion is performed.